Cardiac Conduction System 
 
The cardiac conduction system is the network of specialized muscle cells in the heart that generate and transmit electrical impulses, allowing the heart to beat in a coordinated and rhythmic manner. 
 
Sequence of Conduction (Step-by-Step) 
 
SA node fires → atrial depolarization → atrial contraction 
Impulse reaches AV node → brief delay 
Impulse travels through AV bundle (Bundle of His) 
Signal splits into right and left bundle branches 
Impulse spreads through Purkinje fibers → ventricular depolarization and contraction 
 
The main components and their functions: 
 
 1. Sinoatrial (SA) Node 
Location: Wall of the right atrium near the opening of the superior vena cava 
Function: Acts as the natural pacemaker of the heart generating each heartbeat; creates sinus (P wave)
Normal rate: ~60–100 beats per minute 
 
 2. Atrioventricular (AV) Node 
Location: Lower part of the interatrial septum, near the tricuspid valve 
Function: Delays the electrical signal briefly to allow the atria to contract fully and fill the ventricles before they contract; creates QRS
Normal rate: 40-60 beats per minute 
 
 3. Atrioventricular (AV) Bundle (Bundle of His) 
Location: Extends from the AV node into the interventricular septum 
Function: The only electrical connection between the atria and ventricles, conducting impulses from the AV node to the ventricles 
 
4. Right and Left Bundle Branches 
Location: Run along the interventricular septum 
Function: Carry impulses down to the apex of the heart, toward the respective ventricles 
 
 5. Purkinje Fibers 
Location: Spread throughout the ventricular myocardium 
Function: Conduct impulses rapidly to all parts of the ventricles, causing them to contract almost simultaneously 
 
 
 
Clinical Relevance 
 
ECG (Electrocardiogram): Measures electrical activity (conduction) of this system  
 
Cardiac Arrhythmias (abnormal heart rhythms): Occur when conduction is abnormal 
 
For example: 
SA node failure → junctional rhythms (absent p waves) 
AV block → delayed or absent ventricular contraction (note lower heart rate for rhythms generated at the AV node (<60)